McKeown Ryan, Ostilla-Mónico Rodolfo, Pumir Alain, Brenner Michael P, Rubinstein Shmuel M
School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA.
Sci Adv. 2020 Feb 28;6(9):eaaz2717. doi: 10.1126/sciadv.aaz2717. eCollection 2020 Feb.
The essence of turbulent flow is the conveyance of energy through the formation, interaction, and destruction of eddies over a wide range of spatial scales-from the largest scales where energy is injected down to the smallest scales where it is dissipated through viscosity. Currently, there is no mechanistic framework that captures how the interactions of vortices drive this cascade. We show that iterations of the elliptical instability, arising from the interactions between counter-rotating vortices, lead to the emergence of turbulence. We demonstrate how the nonlinear development of the elliptical instability generates an ordered array of antiparallel secondary filaments. The secondary filaments mutually interact, leading to the formation of even smaller tertiary filaments. In experiments and simulations, we observe two and three iterations of this cascade, respectively. Our observations indicate that the elliptical instability could be one of the fundamental mechanisms by which the turbulent cascade develops.
湍流的本质是能量通过在广泛空间尺度上涡旋的形成、相互作用和消散来进行传输，这些空间尺度从能量注入的最大尺度到通过粘性耗散能量的最小尺度。目前，尚无一个机制框架能够描述涡旋相互作用如何驱动这种级联过程。我们表明，反向旋转涡旋之间的相互作用所产生的椭圆不稳定性的迭代会导致湍流的出现。我们展示了椭圆不稳定性的非线性发展如何产生一系列有序的反平行次级细丝。次级细丝相互作用，导致形成更小的三级细丝。在实验和模拟中，我们分别观察到了这种级联的两次和三次迭代。我们的观察表明，椭圆不稳定性可能是湍流级联发展的基本机制之一。
